1. Field of the Invention
The present invention relates to an information storage medium on which information is recorded upon radiation of a light beam and, more particularly, to an information storage medium having a recording layer containing Te.
2. Description of the Related Art
An information storage medium having a recording layer consisting of Te is known as a conventional information medium, such as an optical disk, on which information is recorded upon radiation of a laser beam, and from which the recorded information is reproduced.
Te, however, has poor durability in the outer atmosphere, and is susceptible to oxidation especially under conditions of high temperature and humidity.
In order to eliminate such drawbacks, an information storage medium has been proposed (U.S. Pat. No. 4,433,340) having a recording layer consisting of Te as a major element and also containing carbon and hydrogen (to be referred to as a Te-C film hereinafter).
The Te-C film is formed by performing sputtering in an atmosphere containing a hydrocarbon gas such as CH.sub.4, using Te as a target, and has an amorphous structure immediately after it is formed (M. Mashita and N. Yasuda, Processing of SPIE, 329, 190 (1982)).
Because the Te-C film is formed such that Te clusters are dispersed throughout the film, it has an oxidation resistance superior to that of a film composed only of Te.
However, in conditions of high temperature in particular, the Te clusters in a Te-C film tend to coagulate, with the result that the Te is crystallized, and a C-H matrix is converted into a gas which is discharged through the surface of the recording layer, coarsening the surface of the layer thereby changing its surface reflectance and increasing the error rate during reproduction of information.
In the meantime, widespread demand for higher data processing speeds has necessitated that information be recorded on optical disks, which are rotated at high speed.
If, however, an optical disk using a conventional Te-C film is rotated at high speed, satisfactory recording may not be performed because a radiation time of a laser beam is too short.
In addition, if the C content of a Te-C film is increased, its record sensitivity is decreased.